Hunting K3 subRX gremlins

[Gary Hinson]

Dear Elecrafties,

Does anyone have any idea why my subRX might be intermittent on 40m?  

Sometimes, for no obvious reason, all I get is hiss in my right ear, no
sigs.  As far as I have noticed so far, it only happens on 40m.  I don't
think it's the subRX attentuator/preamp, antenna, RF gain or filter
settings.  On Thursday when I first noticed it, I re-calibrated the subRX
synth (among other things) and the gremlins went back into hiding, but not
for long: this afternoon, the gremlins returned.  Earlier this evening I
tried various things such as power-cycling the rig, meddling with the subRX
settings, changing bands and then returning to 40, but still just hiss.
Tonight after dinner, I returned to the rig (still powered up) and the
gremlins have crept back into hiding: the subRX is working again on 40 but I
fear they're just teasing me now.

Any clues about where to hunt first after "... 98, 99, 100 coming ready or
not!"?

73
Gary  ZL2iFB

PS  Also, is the subRX meant to work cross-band with the current/latest
firmware?  CONFIG: VFO IND won't budge from "no" (it just says "UNAVAIL"
when I try to change it).

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[Bill W4ZV]

ZL2IFB:
>Does anyone have any idea why my subRX might be intermittent on 40m?

I would look for an intermittent solder joint in the 40/60m section of the KRX3's BPF (Appendix B, next to last schematic .pdf below).  I would try resoldering all joints in that section.

http://www.elecraft.com/manual/K3_Schematics_Oct2008.pdf

73,  Bill  W4ZV

[Bill W4ZV]

On Mon, Apr 20, 2009 at 9:28 AM, Gary Hvizdak <[hidden email]> wrote:

>     I would suggest that before you pick up your soldering iron, that you
> first inspect all of the toroid solder connections in the 40/60m BPF using
> good lighting an a “good” B&L 7x jeweler’s loupe.  Otherwise, you might only
> be hiding the problem under more solder instead of locating and correcting
> it.  Look for “suspicious” solder connections, and specifically look for
> toroid leads where you see insulation rather than bare wire entering a
> through-hole, rather than bare tinned wire.

That's excellent advice from Gary!  With #1361 I was failing the TX
Gain Calibration on 60m only.  I found one toroid had exactly the
problem he describes (looking from the component side of the board).
I took an X-Acto knife, scraped the toroid leads to expose bare wire
and resoldered from the component side, which fixed the problem.

73,  Bill  W4ZV
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